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Help: Variable On/Off Timer

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New Member
Hi everyone. I sure hope I'm not posting a question that has already been answered a billion times but here goes.

My plans are to build an on/off timer that has a variable "on" time as well as a variable "off" time. On times would be selected from ¼ sec, ½ sec, 1 sec, 2sec and 4 seconds (I think this can be accomplished using a voltage divider network and a rotary selector switch). Off time intervals would be selected from 1 sec, 2sec, 4sec, 6sec, 8sec and 10 seconds (same voltage divider network). When the timer is on it will supply +4.5VDC and when the timer is off it will of course supply zero. I am sure this can be done with a PIC, but I'd rather not go that route. I think this can be accomplished using one or two 555 timers, but I just can't wrap my head around it. I have experience building circuits off of a schematic, but when it comes to the design aspects, I am rather limited.

As for input power I have a 120VAC power supply supplying +24VDC (3A max) that I would like to use and then step the voltage down to the desired pulsing output voltage before entering the timer circuit.

I am really hoping someone can point me in the right direction here. If it sounds like I am asking someone to just plop a schematic I do apologize. Not asking for a hand out, just need to be pointed in the right direction. Thanks!


Well-Known Member
Most Helpful Member
You might start by looking at some of the many 555 tutorials (just Google) such as LM555 Timer Circuits or 555 Timer/Oscillator Tutorial. You would need two timers operating in the monostable mode. One timer would be the "on' time and the other the "off" time. The two timers could trigger an RS flip-flop on and off (the FF can also be made with a 555).
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